Murmur occurs due to defect in

Options

A. AV node
B. SA node
C. Purkinje fibres
D. Heart valves

Answer

### Step-by-Step Solution

1. **Understanding Murmurs**: A murmur is defined as an abnormal sound produced by the flow of blood within the heart. It is important to note that murmurs are not normal heart sounds; they indicate some form of irregularity.

2. **Identifying the Cause of Murmurs**: Murmurs typically occur due to defects or abnormalities in the heart valves. These defects can lead to turbulent blood flow, which creates the characteristic sound of a murmur.

3. **Normal Heart Sounds**: Normal heart sounds are referred to as "lub" and "dub." The "lub" sound occurs when the tricuspid and mitral (bicuspid) valves close, while the "dub" sound occurs when the semilunar valves close. Murmurs occur in addition to these normal sounds.

4. **Characteristics of Murmur Sounds**: Murmurs are often described as a "whooshing" sound, which is different from the normal "lub-dub" sounds of the heart. This whooshing sound is indicative of the turbulent blood flow caused by the defective heart valves.

5. **Evaluating the Options**:
- Atrioventricular (AV) node: Incorrect, as it is involved in electrical conduction, not blood flow.
- Sinoatrial (SA) node: Incorrect, as it also relates to electrical activity, not the physical flow of blood.
- Purkinje fibers: Incorrect, as they are part of the conduction system of the heart.
- Heart valves: Correct, as defects in heart valves lead to the abnormal sounds known as murmurs.

6. **Conclusion**: Therefore, murmurs occur due to defects in the heart valves.